The designs of personal care absorbent products have gone through extensive changes in recent times. Personal care absorbent products include such items as diapers, training pants, incontinence garments, sanitary napkins, bandages and the like. A major thrust in the design of these products, especially with diapers, training pants, incontinence garments and sanitary napkins, has been a reduction in the size of the products while increasing their absorptive capacity. Greater and greater usage of superabsorbents has made this possible.
Using diapers as an example, originally diapers were very thick in design due to the high volumes of fluff or wood pulp used to form the absorbent core of the diaper. As a result, the diapers were very bulky and they tended to leak because, as the absorbent fluff was wetted with urine, the fluff tended to collapse. Typically the fluff used in such personal care absorbent products had a liquid gram per gram capacities of 4 to 20 grams of aqueous liquid absorbed per gram of fluff. In addition, this capacity was dependent upon the amount of pressure being applied to the wet fluff. For example, at a pressure of 0.5 pounds per square inch (psi) the fluff would only hold approximately 7 grams per gram. At 0.1 psi the capacity would increase to approximately 12 grams per gram and at zero psi the capacity would be approximately 20 grams of liquid per gram of fluff.
With the advent of superabsorbents and their incorporation into absorbent cores, the size of the absorbent cores have been reduced. Initial superabsorbents had gram per gram capacities in the range of 50 grams per gram but the particles became very mushy when wet and would often cause gel blocking. Today, superabsorbents have higher absorbency while under load but to do this, many of the superabsorbents have had their capacities reduced to around 35 grams per gram. The first commercial diapers using superabsorbents incorporated from about 10 to 20 percent by weight superabsorbent, based upon the total weight of the absorbent core. The superabsorbent particles, which typically had 20 to 1,000 micron diameters, were contained within the absorbent cores through mechanical entanglement with the wood pulp fibers. In addition, paper tissue was sometimes wrapped around the superabsorbent-containing batts and sometimes the tissue was glued to itself and/or the fluff to further encapsulate and retain the fluff and superabsorbent.
Today, personal care absorbent products such as diapers have greatly reduced their thickness by removing large quantities of the fluff and replacing it with higher and higher percentages of superabsorbent particles. Some of the diapers today have absorbent cores with over 40 percent superabsorbent. Oftentimes the absorbent cores are compressed to further reduce their thickness after adding the tissue wrap. As a result, while old fluff cores tended to collapse when wetted, the new absorbent cores with superabsorbent tend to swell as they are wetted. This swelling coupled with the twisting and flexing the absorbent core experiences during use, can cause the paper tissue wrap to rip and tear, especially when wetted. When this happens, there is a greater chance that the superabsorbent will escape from the diaper. While this is not dangerous, it is not desirable from an overall product performance standpoint.
In the dry state, there is also greater potential for loss of the superabsorbent from the absorbent core as the percentages of superabsorbent are increased. With less fluff in the core, there is less mechanical entrapment of the fibers. Thus, if there is a rip in the paper tissue wrap or a portion of the glued seam becomes separated, there is a higher likelihood that some of the superabsorbent particles will escape. An even bigger problem is that the pores in many paper tissue wraps are too big and therefore allow the superabsorbent to escape. Consequently, there is a need for a more effective way of encapsulating the absorbent core.
From a processing standpoint there are also problems. Gluing a paper tissue wrap is messy and adds cost. Shake out of the superabsorbent particles can also cause equipment and housekeeping problems and higher production costs due to wasted material. As a result, there is a need for an improved absorbent core/wrap for uses such as in personal care absorbent products.